Can you open the 'Console application', and send me what happens when SAMSC opens?
It prints out loads of information to try and tell me whats going on.
There may be a driver conflict with something else in your system.
Catalyst uses bog standard normal quicktime to do its audio playback - nothing fancy.

i may have a delta card lying around. ill see if i can find it.
but i dont have a working g4 without a bit of grief.

The most reliable interface i found so far was the M-audio firewire 410.

This worked on my fully loaded g5, with scsi and blackmagic cards, when the motu 828 just crashed the computer the whole time.
The crashes i had with the 828 mk2 were not caused by my software, but by driver conflicts.